#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
int fac(int a)
{
	if (a == 1)
		return 1;
	else return a + fac(a - 1);
}
int main()
{
	int a = 0;
	scanf("%d", &a);
	printf("%d", fac(a));
	return 0;
}